If I understood correctly, you wish to create a bootable flash drive and copy the image file of Windows while still using Command Prompt. Is that so? I would recommend you to create the bootable drive by using the following commands:
Diskpart
List disk
Select disk n(n is the number of the drive)
Clean
Create partition primary
Select partition 1
Active
Format fs=ntfs
Exit

After that, I recommend you to manually copy your Windows setup files to your USB drive. Please, let me know if this works.